Commercial aircraft typically employ an environmental control system to pressurize a passenger cabin of the aircraft and/or thermal anti-icing systems to provide heated air for anti-icing applications. These systems are commonly powered with bleed air. As used herein, bleed air is defined as compressed air that is extracted from a compressor of a gas turbine engine of the aircraft. The bleed air is bled from a bleed port in a housing of the engine. However, bleed air pressures vary greatly with operating conditions such as, for example, engine speed, operating altitude, etc. To ensure the bleed air has sufficient pressure and/or temperature to power various systems of the aircraft, bleed air is often extracted from a higher stage of the compressor that provides bleed air having a pressure and/or temperature above that demanded by the various systems. Therefore, because the bleed air often exceeds a temperature and pressure thresholds of the aircraft systems, the bleed air is cooled and/or reduced in pressure prior to supplying the air to, for example, the ECS.
To reduce the bleed air temperature, commercial aircraft typically employ a heat exchanger (e.g., a precooler) through which bleed air passes and which is typically located on a pylon adjacent to the engine. A fan operated by the engine of the aircraft provides cool air to the precooler to cool the bleed air prior to supplying the bleed air to the systems of the aircraft. The fan air is often dumped overboard after flowing through the precooler. Thus, cooling the bleed air via the fan reduces the efficiency of the aircraft engine. Additionally, the precooler typically has a relatively large dimensional envelope, which adds extra weight and may require a fan air scoop and exhaust that produce drag. Thus, the relatively large dimensional envelope of the precooler can also affect the efficiency of the aircraft engine. To reduce the bleed air pressure, commercial aircraft typically employ one or more pressure regulating valves through which bleed air passes. Thus, a substantial amount of the energy spent by the engine to produce the bleed air is wasted when cooling the bleed air and/or reducing the pressure of the bleed air. This wasted energy results in greater fuel consumption.
Commercial aircraft that utilize gas turbine engines (e.g., turbo-jet engines) also typically include air turbine starters for starting each of the engines. An air turbine starter includes a turbine that operates to turn a shaft that is mechanically coupled to a drive shaft of the engine. High pressure air supplied by a ground cart or auxiliary power unit is provided to the air turbine starter, which rotates the turbine and causes the drive shaft of the engine to rotate. Bleed air systems and air turbine starter systems generally utilize a large amount of ducting and additional components (e.g., valves, connectors, etc) to operate the respective systems. As a result, these two systems generally add a significant amount of weight to an aircraft engine.